1. Field of the Invention
The present invention concerns a high voltage sectionalizer mechanism which includes an elongated sectionalizer tube and mounting structure having lower electrical contacts arranged for telescopic reception of the tube. The invention includes an actuator connected to a logic circuit of the sectionalizer and positioned to impart, upon firing, drop-out movement of the tube in an essentially pure longitudinal direction in order to immediately shift an upper portion of the tube away from an upper contact and thereby disconnects the circuit without the use of pivotal mounting structure. The sectionalizer mechanism is especially adapted for retrofit installation within the confines of a cabinet of pad-mounted or subsurface switchgear, and is also useful in overhead installations inasmuch as a relatively small cover can be placed over the mechanism to protect the same from the elements.
2. Description of the Prior Art
In high voltage power distribution systems, automatic reclosers or reclosing circuit breakers are often installed in the main supply line near its source of power. The recloser is operable to de-energize the entire system downstream of the recloser if potentially damaging currents above a certain magnitude are detected. After a short period of de-energization, the recloser re-energizes the system unless excessive current conditions are again sensed.
In recent years, increased attention has been directed toward electronic sectionalizers for disabling branch or lateral lines of a distribution system protected by a reclosing circuit breaker. In brief, electronic sectionalizers disconnects lateral lines after a specified number of opening and closing cycles of the reclosing circuit breaker if over-current conditions are detected in the particular lateral line served by the sectionalizer. The sectionalizer disables the lateral line during a dead portion of one of the opening and closing cycles of the reclosing circuit breaker and the lateral line remains in a deactivated state until the problem is corrected and the sectionalizer is re-set. In this manner, current may be automatically and immediately restored to the remaining lateral lines during a subsequent closing cycle of the reclosing circuit breaker.
Certain electronic sectionalizers known in the art are physically interchangable with conventional, overhead cutouts so that sectionalizer can be installed on a retrofit basis in existing cutout mounting structure. These types of sectionalizers include an elongated, electrically conductive tube engageable with upper and lower contacts of the cutout mounting structure, and a logic circuit carried by the tube is arranged to sense the flow of current along the tube and fire an actuator for swinging drop-out of the tube away from the upper contact of the mounting structure and toward an isolated or open circuit position.
Sectionalizers such as those described in U.S. Pat. Nos. 4,553,188 and 4,636,764 are provided with a pivot mechanism that causes the upper portion of the sectionalizer tube to swing away from the upper contact about a horizontal axis once the actuator is fired. The sectionalizer mechanism illustrated in U.S. Pat. No. 4,553,188 has an actuator that, when fired, engages a latch which then shifts toward a release position and allows the tube to swing toward a drop-out orientation under the influence of a spring and/or the forces of gravity. The pivot mechanism of the sectionalizer shown in U.S. Pat. No. 4,636,764 is in the nature of an over-center toggle arrangement, and an actuator is located to move the sectionalizer tube overcenter when fired whereupon the upper portion of the sectionalizer tube pivots and falls away from the upper contact toward an isolated position.
In a pending U.S. Pat. application filed Sept. 11, 1987, and entitled "Latch and Pivot Mechanism for Electronic Sectionalizer Mounting Structure", Ser. No. 07/095,548, and assigned to the assignee of the present invention, an actuator is positioned such that all of the force exerted by the actuator is directed toward a pivotal member interconnecting the tube and the lower contact, and the tube immediately begins a downward, pivotal drop-out motion simultaneously with firing of the actuator. Substantially all of the force exerted by the actuator is directed toward the pivotal member and causes immediate lateral movement of the sectionalizer tube in order to reliably ensure successful drop-out of the tube regardless of adverse environmental conditions and with minimal reliance upon springs or the effects of gravity.
While certain of the aforementioned electronic sectionalizers and pivot mechanisms may be installed on a retrofit basis in existing outdoor, overhead cutout mounting structure, such devices are not a suitable replacement for fuses within many types of pad-mounted or subsurface switchgear. More specifically, there is often not sufficient clearance within the confines of the metal cabinet of pad-mounted and subsurface switchgear to allow the sectionalizer to move laterally and swing in an arc during its drop-out motion when fault currents are detected. As a consequence, a need exists for an electronic sectionalizer which requires smaller operating clearances than the clearances necessary for satisfactory operation of devices that are currently known.